Abbreviations a -autocorrelation length, c -structural semivariance, DOY -day of year, DOYn -normalized day of year, ME -NashSutcliffe model efficiency coefficient, PCA -principal component analysis, psill -partial sill, R s -soil CO 2 efflux, sdstandard deviation, SSErr -residual sum of squares, SWC -soil water content, SWCn -normalized soil water content, TOCtotal organic carbon content, T s -soil temperature, y0 -nugget variance
AbstractIn this study eight temperate grassland sites were monitored for soil CO 2 efflux (R s ) and the spatial covariates soil water content (SWC) and soil temperature (T s ) at fine scale in over 77 measurement campaigns. The goals of this multisite study were to explore the correlations between environmental gradients and spatial patterns of R s , SWC and T s , which are not site-specific and to quantify the relevance of biotic and abiotic controls over spatial patterns along increasing vegetation structural complexity. These patterns in water-limited ecosystems in East-Central Europe are likely to be influenced by summer droughts caused by the changing climate.A consistent experimental setup was applied at the study sites including 75 sampling locations along 15 m circular transects. Spatial data processing was mainly based on variography. Two proxy variables were introduced to relate the site characteristics in terms of soils, water status and vegetation. Normalized SWC (SWCn) reconciled site-specific soil water regimes while normalized day of year integrated temperature and vegetation phenology.A principal component analysis revealed that the progressing closure of vegetation in combination with large R s and SWCn values, as well as low T s and R s variability support the detectability of spatial patterns found in both the abiotic and biotic variables. Our results showed that apart from SWC the pattern of soil temperature also had an effect on spatial structures. We detected that when the spatially 2 structured variability of T s was low, a strong negative correlation existed between SWCn and the spatial autocorrelation length of R s with r=0.66 (p<0.001). However, for high spatially structured variability of T s , occurring presumably at low T s in spring and autumn, the correlation did not exist and it was difficult to quantify the spatial autocorrelation of R s . Our results are indicative of a potential shift from homogeneity and dominance of biotic processes to an increased heterogeneity and abiotic regulation in drought prone ecosystems under conditions of decreasing soil moisture.